The changing epidemiology of Kunjin virus in Australia

Lessons Learned from West Nile Virus Infection:Vaccinations in Equines and Their Implications for One Health Approaches

Humans and equines are two dead-end hosts of the mosquito-borne West Nile virus (WNV) with similar susceptibility and pathogenesis. Since the introduction of WNV vaccines into equine populations of the United States of America (USA) in late 2002, there have been only sporadic cases of WNV infection in equines. These cases are generally attributed to unvaccinated and under-vaccinated equines. In contrast, due to the lack of a human WNV vaccine, WNV cases in humans have remained steadily high. An average of 115 deaths have been reported per year in the USA since the first reported case in 1999. Therefore, the characterization of protective immune responses to WNV and the identification of immune correlates of protection in vaccinated equines will provide new fundamental information about the successful development and evaluation of WNV vaccines in humans. This review discusses the comparative epidemiology, transmission, susceptibility to infection and disease, clinical manifestation and pathogenesis, and immune responses of WNV in humans and equines. Furthermore, prophylactic and therapeutic strategies that are currently available and under development are described. In addition, the successful vaccination of equines against WNV and the potential lessons for human vaccine development are discussed.

Development and evaluation of an easy to use real-time reverse-transcription loop-mediated isothermal amplification assay for clinical diagnosis of West Nile virus

West Nile Virus (WNV) causes a serious public health concern in many countries around the world. Virus detection in pathological samples is a key component of WNV infection diagnostic, classically performed by real-time PCR. In outbreak situation, rapid detection of the virus, in peripheral laboratories or at point of care, is crucial to guide decision makers and for the establishment of adequate action plans to prevent virus dissemination. Here, we evaluate a Loop-mediated isothermal amplification (LAMP) tool for WNV detection. Amplifications were performed comparatively on extracted viral RNA and on crude samples using a classical thermal cycler and a portable device (pebble device). qRT-PCR was used as gold standard and two sets of urine samples (n = 62 and n = 74) were used to evaluate the retained amplification protocols and assess their sensitivity and specificity. RT-LAMP on RNA extracts and crude samples showed a sensitivity of 90 % and 87 %, respectively. The specificity was 100 % for extracts and 97 % for crude samples. Using the device, the RT-LAMP on extracted RNA was comparable to the gold standard results (100 % sensitivity and specificity) and it was a bit lower on crude samples (65 % sensitivity and 94 % specificity). These results show that RT-LAMP is an efficient technique to detect WNV. RT-LAMP provides a rapid, sensitive, high-throughput and portable tool for accurate WNV detection and has potentials to facilitate diagnostic and surveillance efforts both in the laboratory and in the field, especially in developing countries.

An evaluation of the landscape structure and La Niña climatic anomalies associated with Japanese encephalitis virus outbreaks reported in Australian piggeries in 2022

The widespread activity of Japanese encephalitis virus (JEV) reported in previously unaffected regions of eastern and southern Australia in 2022 represents the most significant local arbovirus emergency in almost 50 years. Japanese encephalitis virus is transmitted by mosquitoes and maintained in wild ardeid birds and amplified in pigs, the latter of which suffer significant reproductive losses as a result of infection. The landscape epidemiology of JEV in mainland Australia is almost entirely unknown, particularly in the eastern and southern parts of the country where the virus has not been previously documented. Although other areas with endemic JEV circulation in the Indo-Pacific region have demonstrated the importance of wild waterbird-livestock interface in agricultural-wetland mosaics, no such investigation has yet determined the composition and configuration of pathogenic landscapes for Australia. Moreover, the recent emergence in Australia has followed substantial precipitation and temperature anomalies associated with the La Niña phase of the El Niño Southern Oscillation. This study investigated the landscape epidemiology of JEV outbreaks in Australian piggeries reported between January and April of 2022 to determine the influence of ardeid habitat suitability, hydrogeography, hydrology, land cover and La Niña-associated climate anomalies. Outbreaks of JEV in domestic pigs were associated with intermediate ardeid species richness, cultivated land and grassland fragmentation, waterway proximity, temporary wetlands, and hydrological flow accumulation. This study has identified the composition and configuration of landscape features that were associated with piggery outbreaks reported in 2022 in Australia. Although preliminary, these findings can inform actionable strategies for the development of new One Health JEV surveillance specific to the needs of Australia.

Nucleic Acid Preservation Card Surveillance Is Effective for Monitoring Arbovirus Transmission on Crocodile Farms and Provides a One Health Benefit to Northern Australia

The Kunjin strain of West Nile virus (WNV_KUN) is a mosquito-transmitted flavivirus that can infect farmed saltwater crocodiles in Australia and cause skin lesions that devalue the hides of harvested animals. We implemented a surveillance system using honey-baited nucleic acid preservation cards to monitor WNV_KUN and another endemic flavivirus pathogen, Murray Valley encephalitis virus (MVEV), on crocodile farms in northern Australia. The traps were set between February 2018 and July 2020 on three crocodile farms in Darwin (Northern Territory) and one in Cairns (North Queensland) at fortnightly intervals with reduced trapping during the winter months. WNV_KUN RNA was detected on all three crocodile farms near Darwin, predominantly between March and May of each year. Two of the NT crocodile farms also yielded the detection of MVE viral RNA sporadically spread between April and November in 2018 and 2020. In contrast, no viral RNA was detected on crocodile farms in Cairns during the entire trapping period. The detection of WNV_KUN and MVEV transmission by FTA^TM cards on farms in the Northern Territory generally correlated with the detection of their transmission to sentinel chicken flocks in nearby localities around Darwin as part of a separate public health surveillance program. While no isolates of WNV_KUN or MVEV were obtained from mosquitoes collected on Darwin crocodile farms immediately following the FTA^TM card detections, we did isolate another flavivirus, Kokobera virus (KOKV), from Culex annulirostris mosquitoes. Our studies support the use of the FTA^TM card system as a sensitive and accurate method to monitor the transmission of WNV_KUN and other arboviruses on crocodile farms to enable the timely implementation of mosquito control measures. Our detection of MVEV transmission and isolation of KOKV from mosquitoes also warrants further investigation of their potential role in causing diseases in crocodiles and highlights a “One Health” issue concerning arbovirus transmission to crocodile farm workers. In this context, the introduction of FTA^TM cards onto crocodile farms appears to provide an additional surveillance tool to detect arbovirus transmission in the Darwin region, allowing for a more timely intervention of vector control by relevant authorities.

The epidemiology and outcomes of central nervous system infections in Far North Queensland, tropical Australia; 2000-2019

Background

The epidemiology of central nervous system (CNS) infections in tropical Australia is incompletely defined.

Methods

A retrospective study of all individuals in Far North Queensland, tropical Australia, who were diagnosed with a CNS infection between January 1, 2000, and December 31, 2019. The microbiological aetiology of the infection was correlated with patients’ demographic characteristics and their clinical course.

Results

There were 725 cases of CNS infection during the study period, meningitis (77.4%) was the most common, followed by brain abscess (11.6%), encephalitis (9.9%) and spinal infection (1.1%). Infants (24.3%, p<0.0001) and Aboriginal and Torres Strait Islander Australians (175/666 local residents, 26.3%, p<0.0001) were over-represented in the cohort.

A pathogen was identified in 513 cases (70.8%); this was viral in 299 (41.2%), bacterial in 175 (24.1%) and fungal in 35 (4.8%). Cryptococcal meningitis (24 cases) was diagnosed as frequently as pneumococcal meningitis (24 cases). There were only 2 CNS infections with a S. pneumoniae serotype in the 13-valent pneumococcal vaccine after its addition to the National Immunisation schedule in 2011. Tropical pathogens–including Cryptococcus species (9/84, 11%), Mycobacterium tuberculosis (7/84, 8%) and Burkholderia pseudomallei (5/84, 6%)–were among the most common causes of brain abscess. However, arboviral CNS infections were rare, with only one locally acquired case—a dengue infection in 2009—diagnosed in the entire study period. Intensive Care Unit admission was necessary in 14.3%; the overall case fatality rate was 4.4%.

Conclusion

Tropical pathogens cause CNS infections as commonly as traditional bacterial pathogens in this region of tropical Australia. However, despite being highlighted in the national consensus guidelines, arboviruses were identified very rarely. Prompt access to sophisticated diagnostic and supportive care in Australia’s well-resourced public health system is likely to have contributed to the cohort’s low case-fatality rate.

The RNA Secondary Structure Analysis Reveals Potential for Emergence of Pathogenic Flaviviruses

The Flavivirus genus is divided into four groups: Mosquito-borne flaviviruses, Tick-borne flaviviruses, no-known vector flaviviruses, and Insect specific flaviviruses. Millions of people are affected worldwide every year due to the flaviviral infections. The 5' UTR of the RNA genome plays a critical role in the biology of flaviviruses. To explore any correlation between the topology of the 5' UTR and pathogenesis, a global scale study of the RNA secondary structure of different groups of flaviviruses has been conducted. We found that most of the pathogenic flaviviruses, irrespective of their mode of transmission, tend to form a Y shaped topology in the Stem loop A of the 5' UTR. Some of the current non-pathogenic flaviviruses were also observed to form Y shaped structure. Based on this study, it has been proposed that the flaviviruses having the Y shaped topology in their 5' UTR regions may have the potential to become pathogenic.

Australia's notifiable disease status, 2016: Annual report of the National Notifiable Diseases Surveillance System

Abstract

In 2016, a total of 67 diseases and conditions were nationally notifiable in Australia. The states and territories reported 330,387 notifications of communicable diseases to the National Notifiable Diseases Surveillance System. Notifications have remained stable between 2015 and 2016. In 2016, the most frequently notified diseases were vaccine preventable diseases (139,687 notifications, 42% of total notifications); sexually transmissible infections (112,714 notifications, 34% of total notifications); and gastrointestinal diseases (49,885 notifications, 15% of total notifications). Additionally, there were 18,595 notifications of bloodborne diseases; 6,760 notifications of vectorborne diseases; 2,020 notifications of other bacterial infections; 725 notifications of zoonoses and one notification of a quarantinable disease.

Ross River Virus Infection: A Cross-Disciplinary Review with a Veterinary Perspective

Ross River virus (RRV) has recently been suggested to be a potential emerging infectious disease worldwide. RRV infection remains the most common human arboviral disease in Australia, with a yearly estimated economic cost of $4.3 billion. Infection in humans and horses can cause chronic, long-term debilitating arthritogenic illnesses. However, current knowledge of immunopathogenesis remains to be elucidated and is mainly inferred from a murine model that only partially resembles clinical signs and pathology in human and horses. The epidemiology of RRV transmission is complex and multifactorial and is further complicated by climate change, making predictive models difficult to design. Establishing an equine model for RRV may allow better characterization of RRV disease pathogenesis and immunology in humans and horses, and could potentially be used for other infectious diseases. While there are no approved therapeutics or registered vaccines to treat or prevent RRV infection, clinical trials of various potential drugs and vaccines are currently underway. In the future, the RRV disease dynamic is likely to shift into temperate areas of Australia with longer active months of infection. Here, we (1) review the current knowledge of RRV infection, epidemiology, diagnostics, and therapeutics in both humans and horses; (2) identify and discuss major research gaps that warrant further research.

Mosquito-Borne Viruses and Non-Human Vertebrates in Australia: A Review

Mosquito-borne viruses are well recognized as a global public health burden amongst humans, but the effects on non-human vertebrates is rarely reported. Australia, houses a number of endemic mosquito-borne viruses, such as Ross River virus, Barmah Forest virus, and Murray Valley encephalitis virus. In this review, we synthesize the current state of mosquito-borne viruses impacting non-human vertebrates in Australia, including diseases that could be introduced due to local mosquito distribution. Given the unique island biogeography of Australia and the endemism of vertebrate species (including macropods and monotremes), Australia is highly susceptible to foreign mosquito species becoming established, and mosquito-borne viruses becoming endemic alongside novel reservoirs. For each virus, we summarize the known geographic distribution, mosquito vectors, vertebrate hosts, clinical signs and treatments, and highlight the importance of including non-human vertebrates in the assessment of future disease outbreaks. The mosquito-borne viruses discussed can impact wildlife, livestock, and companion animals, causing significant changes to Australian ecology and economy. The complex nature of mosquito-borne disease, and challenges in assessing the impacts to non-human vertebrate species, makes this an important topic to periodically review.

Climate change and infectious diseases in Australia's Torres Strait Islands

OBJECTIVE

This research seeks to identify climate-sensitive infectious diseases of concern with a present and future likelihood of increased occurrence in the geographically vulnerable Torres Strait Islands, Australia. The objective is to contribute evidence to the need for adequate climate change responses.

METHODS

Case data of infectious diseases with proven, potential and speculative climate sensitivity were compiled.

RESULTS

Five climate-sensitive diseases in the Torres Strait and Cape York region were identified as of concern: tuberculosis, dengue, Ross River virus, melioidosis and nontuberculous mycobacterial infection. The region constitutes 0.52% of Queensland's population but has a disproportionately high proportion of the state's cases: 20.4% of melioidosis, 2.4% of tuberculosis and 2.1% of dengue.

CONCLUSIONS

The Indigenous Torres Strait Islander peoples intend to remain living on their traditional country long-term, yet climate change brings risks of both direct and indirect human health impacts. Implications for public health: Climate-sensitive infections pose a disproportionate burden and ongoing risk to Torres Strait Islander peoples. Addressing the causes of climate change is the responsibility of various agencies in parallel with direct action to minimise or prevent infections. All efforts should privilege Torres Strait Islander peoples' voices to self-determine response actions.

Modeling the West Nile virus transfusion transmission risk in a nonoutbreak country associated with traveling donors

BACKGROUND

West Nile virus (WNV) is a mosquito-borne virus and transfusion transmission (TT) has been demonstrated. The European Union and neighboring countries experience an annual transmission season.

STUDY DESIGN AND METHODS

We developed a novel probabilistic model to estimate the WNV TT risk in Australia attributable to returned donors who had travelled to the European Union and neighboring countries during the 2018. We estimated weekly WNV TT risks in Australia for each outbreak country and the cumulative risk for all countries.

RESULTS

Highest mean weekly TT risk in Australia attributable to donors returning from a specific outbreak country was 1 in 23.3 million (plausible range, 16.8-41.9 million) donations during Week 39 in Croatia. Highest mean weekly cumulative TT risk was 1 in 8.5 million donations (plausible range, 5.1-17.8 million) during Week 35.

CONCLUSIONS

The estimated TT risk in Australia attributable to returning donors from the European Union and neighboring countries in 2018 was very small, and additional risk mitigation strategies were not indicated. In the context of such low TT risks, a simpler but effective approach would be to monitor the number of weekly reported West Nile fever cases and implement risk modeling only when the reported cases reached a predefined number or trigger point.

Neglected Australian Arboviruses Associated With Undifferentiated Febrile Illnesses

Infections with commonly occurring Australian arthropod-borne arboviruses such as Ross River virus (RRV) and Barmah Forest virus (BFV) are diagnosed routinely by pathology laboratories in Australia. Others, such as Murray Valley encephalitis (MVEV) and Kunjin (KUNV) virus infections may be diagnosed by specialist reference laboratories. Although Alfuy (ALFV), Edge Hill (EHV), Kokobera (KOKV), Sindbis (SINV), and Stratford (STRV) viruses are known to infect humans in Australia, all are considered 'neglected.' The aetiologies of approximately half of all cases of undifferentiated febrile illnesses (UFI) in Australia are unknown and it is possible that some of these are caused by the neglected arboviruses. The aims of this study were to determine the seroprevalence of antibodies against several neglected Australian arboviruses among residents of Queensland, north-east Australia, and to ascertain whether any are associated with UFI. One hundred age- and sex-stratified human plasma samples from blood donors in Queensland were tested to determine the prevalence of neutralising antibodies against ALFV, BFV, EHV, KOKV, KUNV, MVEV, RRV, SINV, and STRV. The seroconversion rates for RRV and BFV infections were 1.3 and 0.3% per annum, respectively. The prevalence of antibodies against ALFV was too low to enable estimates of annual infection rates to be determined, but the values obtained for other neglected viruses, EHV (0.1%), KOKV (0.05%), and STRV (0.05%), indicated that the numbers of clinical infections occurring with these agents are likely to be extremely small. This was borne out by the observation that only 5.7% of a panel of 492 acute phase sera from UFI patients contained IgM against any of these arboviruses, as detected by an indirect immunofluorescence assay. While none of these neglected arboviruses appear to be a cause of a significant number of UFIs in Australia at this time, each has the potential to emerge as a significant human pathogen if there are changes to their ecological niches.

The Role of Temperature in Transmission of Zoonotic Arboviruses

We reviewed the literature on the role of temperature in transmission of zoonotic arboviruses. Vector competence is affected by both direct and indirect effects of temperature, and generally increases with increasing temperature, but results may vary by vector species, population, and viral strain. Temperature additionally has a significant influence on life history traits of vectors at both immature and adult life stages, and for important behaviors such as blood-feeding and mating. Similar to vector competence, temperature effects on life history traits can vary by species and population. Vector, host, and viral distributions are all affected by temperature, and are generally expected to change with increased temperatures predicted under climate change. Arboviruses are generally expected to shift poleward and to higher elevations under climate change, yet significant variability on fine geographic scales is likely. Temperature effects are generally unimodal, with increases in abundance up to an optimum, and then decreases at high temperatures. Improved vector distribution information could facilitate future distribution modeling. A wide variety of approaches have been used to model viral distributions, although most research has focused on the West Nile virus. Direct temperature effects are frequently observed, as are indirect effects, such as through droughts, where temperature interacts with rainfall. Thermal biology approaches hold much promise for syntheses across viruses, vectors, and hosts, yet future studies must consider the specificity of interactions and the dynamic nature of evolving biological systems.

West Nile Virus Associations in Wild Mammals: An Update

Although West Nile virus (WNV) is generally thought to circulate among mosquitoes and birds, several historic and recent works providing evidence of WNV activity in wild mammals have been published. Indeed, a previous review tabulated evidence of WNV exposure in at least 100 mammalian species. Herein, we provide an update on WNV activity in wild and select other mammals that have been reported since the last major review article on this subject was published in early 2013. Of interest, new species, such as Hoffman’s two-toed sloths (Choloepus hoffmanni), are now included in the growing list of wild mammals that have been naturally exposed to WNV. Furthermore, new instances of WNV viremia as well as severe disease presumably caused by this virus have been reported in wild mammals (e.g., the Virginia opossum [Didelphis virginiana]) from natural and semi-captive (e.g., zoological institution) settings. Regrettably, few recent challenge studies have been conducted on wild mammals, which would provide key information as to their potential role(s) in WNV cycles. Largely based on these recent findings, important future lines of research are recommended to assess which mammalian species are commonly exposed to WNV, which mammal species develop viremias sufficient for infecting mosquitoes, and which mammal species might be negatively affected by WNV infection at the species or population level.

Evaluation of real-time reverse-transcription loop-mediated isothermal amplification assay for clinical diagnosis of West Nile virus in patients

Background & objectives

West Nile virus (WNV) is a mosquito-borne flavivirus. The disease can be diagnosed by isolation followed by fluorescent antibody tests, enzyme-linked immunosorbent assay and polymerase chain reaction (PCR) assay. These diagnostic methods are laborious and time-consuming. The present study was aimed to evaluate the real-time reverse-transcription loop-mediated isothermal amplification (RT-LAMP) method for rapid, early and accurate diagnosis of WNV.

Methods

A one-step single tube accelerated quantitative RT-LAMP assay was evaluated by targeting the Env gene of WNV. The gene amplification was accomplished by incubating the reaction mixture at 63°C for 60 min in both real time turbidimeter as well as routine laboratory water bath/dry heating bath. To rule out contamination issues, proper negative controls, including no template, no primer; and no enzyme, were always kept alongside each run. The RT-LAMP assay was evaluated on 105 clinical samples from individuals having ocular infection.

Results

Of the 105 samples tested, 27 were positive for WNV by RT-LAMP assay. The comparative evaluation with conventional RT-PCR revealed 100 per cent accordance with sensitivity and specificity of 100 and 95 per cent, respectively. The specificity of this assay was confirmed with serum samples obtained from patients with dengue and chikungunya.

Interpretation & conclusions

The RT-LAMP test seemed to be a sensitive and specific method for rapid detection of WNV infection and would be useful for rapid screening of a large number of clinical samples in endemic areas during outbreaks.

Unexpected outbreaks of arbovirus infections: lessons learned from the Pacific and tropical America

Pandemic arboviruses have emerged as a major global health problem in the past four decades. Predicting where and when the next arbovirus epidemic will occur is a challenge, but history suggests that arboviral black swan events (epidemics that are difficult to predict and that have an extreme effect) will continue to occur as urban growth and globalisation expand. We briefly review unexpected arbovirus epidemics that have occurred in the past 50 years, with emphasis on the American and Pacific regions, to illustrate their unpredictability, and to highlight the need for improved global preparedness, including laboratory-based surveillance, prevention, and control programmes.

Virulence and Evolution of West Nile Virus, Australia, 1960-2012

Despite the absence of disease in humans and animals, virulent virus strains have been circulating for >30 years.

Worldwide, West Nile virus (WNV) causes encephalitis in humans, horses, and birds. The Kunjin strain of WNV (WNV_KUN) is endemic to northern Australia, but infections are usually asymptomatic. In 2011, an unprecedented outbreak of equine encephalitis occurred in southeastern Australia; most of the ≈900 reported cases were attributed to a newly emerged WNV_KUN strain. To investigate the origins of this virus, we performed genetic analysis and in vitro and in vivo studies of 13 WNV_KUN isolates collected from different regions of Australia during 1960–2012. Although no disease was recorded for 1984, 2000, or 2012, isolates collected during those years (from Victoria, Queensland, and New South Wales, respectively) exhibited levels of virulence in mice similar to that of the 2011 outbreak strain. Thus, virulent strains of WNV_KUN have circulated in Australia for >30 years, and the first extensive outbreak of equine disease in Australia probably resulted from a combination of specific ecologic and epidemiologic conditions.

Neurological disease caused by flavivirus infections

The Flavivirus genus contains dozens of species with varying geographical distributions. Most flavivirus infections in humans are asymptomatic or manifest as a non-specific febrile illness, sometimes accompanied by rash or arthralgia. Certain species are more commonly associated with neurological disease and may be termed neurotropic flaviviruses. Several flaviviruses endemic to Australia and our near northern neighbours are neurotropic, such as Murray Valley encephalitis virus, West Nile (Kunjin) virus and Japanese encephalitis virus. Flavivirus neurological disease ranges from self-limiting meningitis to fulminant encephalitis causing permanent debilitating neurological sequelae or death. The recent Zika virus outbreak in South America has highlighted the dramatic effects of flavivirus neurotropism on the developing brain. This article focuses on the neurotropic flaviviruses endemic to Australia and those of international significance.

Helicase Domain of West Nile Virus NS3 Protein Plays a Role in Inhibition of Type I Interferon Signalling

West Nile virus (WNV) is a neurotropic flavivirus that can cause encephalitis in mammalian and avian hosts. In America, the virulent WNV strain (NY99) is causing yearly outbreaks of encephalitis in humans and horses, while in Australia the less virulent Kunjin strain of WNV strain has not been associated with significant disease outbreaks until a recent 2011 large outbreak in horses (but not in humans) caused by NSW2011 strain. Using chimeric viruses between NY99 and NSW2011 strains we previously identified a role for the non-structural proteins of NY99 strain and especially the NS3 protein, in enhanced virus replication in type I interferon response-competent cells and increased virulence in mice. To further define the role of NY99 NS3 protein in inhibition of type I interferon response, we have generated and characterised additional chimeric viruses containing the protease or the helicase domains of NY99 NS3 on the background of the NSW2011 strain. The results identified the role for the helicase but not the protease domain of NS3 protein in the inhibition of type I interferon signalling and showed that helicase domain of the more virulent NY99 strain performs this function more efficiently than helicase domain of the less virulent NSW2011 strain. Further analysis with individual amino acid mutants identified two amino acid residues in the helicase domain primarily responsible for this difference. Using chimeric replicons, we also showed that the inhibition of type I interferon (IFN) signalling was independent of other known functions of NS3 in RNA replication and assembly of virus particles.

Characterization of non-lethal West Nile Virus (WNV) infection in horses: Subclinical pathology and innate immune response

Most natural West Nile virus (WNV) infections in humans and horses are subclinical or sub-lethal and non-encephalitic. Yet, the main focus of WNV research remains on the pathogenesis of encephalitic disease, mainly conducted in mouse models. We characterized host responses during subclinical WNV infection in horses and compared outcomes with those obtained in a novel rabbit model of subclinical WNV infection (Suen et al. 2015. Pathogens, 4: 529). Experimental infection of 10 horses with the newly emerging WNV-strain, WNV_NSW2011, did not result in neurological disease in any animal but transcriptional upregulation of both type I and II interferon (IFN) was seen in peripheral blood leukocytes prior to or at the time of viremia. Likewise, transcript upregulation for IFNs, TNFα, IL1β, CXCL10, TLRs, and MyD88 was detected in lymphoid tissues, while IFNα, CXCL10, TLR3, ISG15 and IRF7 mRNA was upregulated in brains with histopathological evidence of mild encephalitis, but absence of detectable viral RNA or antigen. These responses were reproduced in the New Zealand White rabbits (Oryctolagus cuniculus) experimentally infected with WNV_NSW2011, by intradermal footpad inoculation. Kinetics of the anti-WNV antibody response was similar in horses and rabbits, which for both species may be explained by the early IFN and cytokine responses evident in circulating leukocytes and lymphoid organs. Given the similarities to the majority of equine infection outcomes, immunocompetent rabbits appear to represent a valuable small-animal model for investigating aspects of non-lethal WNV infections, notably mechanisms involved in abrogating morbidity.

Archival Isolates Confirm a Single Topotype of West Nile Virus in Australia

West Nile virus is globally wide-spread and causes significant disease in humans and animals. The evolution of West Nile virus Kunjin subtype in Australia (WNV_KUN) was investigated using archival samples collected over a period of 50 years. Based on the pattern of fixed amino acid substitutions and time-stamped molecular clock analyses, a single long-term lineage (or topotype) was inferred. This implies that a bottleneck exists such that regional strains eventually die out and are replaced with strains from a single source. This was consistent with current hypotheses regarding the distribution of WNV_KUN, whereby the virus is enzootic in northern Australia and is disseminated to southern states by water-birds or mosquitoes after flooding associated with above average rainfall. In addition, two previous amino acid changes associated with pathogenicity, an N-Y-S glycosylation motif in the envelope protein and a phenylalanine at amino acid 653 in the RNA polymerase, were both detected in all isolates collected since the 1980s. Changes primarily occurred due to stochastic drift. One fixed substitution each in NS3 and NS5, subtly changed the chemical environment of important functional groups, and may be involved in fine-tuning RNA synthesis. Understanding these evolutionary changes will help us to better understand events such as the emergence of the virulent strain in 2011.

West Nile virus is endemic in Australia, and is considered benign in relation to strains that circulate globally. In 2011, a more pathogenic variant emerged which caused disease in horses. To understand the evolution of the virus, and as a background to the emergence of the pathogenic strain, we used high throughput sequencing combined with bioinformatics tools to obtain an overview of the evolution of the virus over 50 years. A single lineage regardless of the collection site was apparent. This was also supported by the pattern of changes in sequence between the isolates. The most significant finding was that the single lineage nature of the virus’s evolution infers that regional strains circulate for some years before becoming extinct. The regional strains must then be replaced by continual re-seeding, most likely by waterbirds that disseminate the virus across the continent after above average rainfall. There were changes in the nucleotide sequence that had become established at a population level. These were related to the structure of the viral proteins: in particular the envelope protein, the helicase (NS3) and methyltransferase domain of NS5. There were two changes in catalytic domains which may indicate some fine-tuning of replication.

The Impact of Prior Flavivirus Infections on the Development of Type 2 Diabetes Among the Indigenous Australians

It is estimated that 5% of Australians over the age of 18 have diabetes, with the number of new cases increasing every year. Type 2 diabetes (T2D) also represents a significant disease burden in the Australian indigenous population, where prevalence is three times greater than that of non-indigenous Australians. Prevalence of T2D has been found to be higher in rural and remote indigenous Australian populations compared with urban indigenous Australian populations. Several studies have also found that body mass index and waist circumference are not appropriate for the prediction of T2D risk in indigenous Australians. Regional and remote areas of Australia are endemic for a variety of mosquito-borne flaviviruses. Studies that have investigated seroprevalence of flaviviruses in remote aboriginal communities have found high proportions of seroconversion. The family Flaviviridae comprises several genera of viruses with non-segmented single-stranded positive sense RNA genomes, and includes the flaviviruses and hepaciviruses. Hepatitis C virus (HCV) has been shown to be associated with insulin resistance and subsequent development of T2D. Flaviviruses and HCV possess conserved proteins and subgenomic RNA structures that may play similar roles in the development of insulin resistance. Although dietary and lifestyle factors are associated with increased risk of developing T2D, the impact of infectious diseases such as arboviruses has not been assessed. Flaviviruses circulating in indigenous Australian communities may play a significant role in inducing glucose intolerance and exacerbating T2D.

A Survey of Knowledge, Attitudes, and Practices in Relation to Mosquitoes and Mosquito-Borne Disease in Western Australia

On average, more than 1,000 individuals will acquire a mosquito-borne disease in Western Australia (WA) each year. Knowledge, attitudes, and practices (KAP) in relation to mosquitoes and mosquito-borne disease have not yet been investigated within Australia. A randomized telephone survey of 2,500 households across 12 regions in WA was undertaken between February and May 2014. The aim of the survey was to obtain baseline KAP data surrounding mosquitoes and mosquito-borne diseases in different regions of WA, across a range of age groups and between males and females. The results of this survey indicate that the majority of respondents are aware of the potential for mosquitoes in WA to transmit Ross River virus, while awareness of other endemic mosquito-borne diseases remains limited. Common misconceptions exist in relation to exotic mosquito-borne diseases, with respondents incorrectly identifying malaria and dengue as endemic diseases in WA. The survey also highlighted a range of important issues, such as limited awareness of the potential for backyard breeding in domestic containers, occupational exposure to mosquitoes in regions with a large employment base in the mining and resources sector, increased exposure to mosquitoes as a result of participation in outdoor recreational activities in the north of the State, and reduced awareness of mosquito-borne disease in individuals aged 18-34 years. The results of this study will be used to inform the development of a new communication strategy by the Department of Health, to further raise awareness of mosquito-borne disease in WA. The data will then provide a baseline against which to compare future survey results, facilitating the rigorous evaluation of new communication efforts.

The E glycoprotein plays an essential role in the high pathogenicity of European-Mediterranean IS98 strain of West Nile virus

West Nile virus (WNV) is the most widespread arbovirus in the world. Several recent outbreaks and epizootics have been reported in Europe and the Mediterranean basin with increased virulence. In contrast to the well-characterized American and Australian strains, little is known about the virulence determinants of the WNV European-Mediterranean strains. To investigate the viral factors involved in the virulence of these strains, we generated chimeras between the highly neuropathogenic Israel 1998 (IS-98-ST1, IS98) strain and the non-pathogenic Malaysian Kunjin virus (KJMP-502). In vivo analyses in a mouse model of WNV pathogenesis shows that chimeric virus where KJMP-502 E glycoprotein was replaced by that of IS98 is neuropathogenic, demonstrating that this protein is a major virulence determinant. Presence of the N-glycosylation site had limited impact on virus virulence and the 5'UTR does not seem to influence pathogenesis. Finally, mice inoculated with KJMP-502 virus were protected against lethal IS98 infection.

Acute Flaccid Paralysis: The New, The Old, and The Preventable

Acute flaccid paralysis (AFP) has a changing epidemiology with ongoing polio outbreaks and emerging causes such as nonpolio enteroviruses and West Nile virus (WNV). We report a case of AFP from the Horn of Africa that was initially classified as probable polio but subsequently found to be due to WNV.

Climate change impacts on West Nile virus transmission in a global context

West Nile virus (WNV), the most widely distributed virus of the encephalitic flaviviruses, is a vector-borne pathogen of global importance. The transmission cycle exists in rural and urban areas where the virus infects birds, humans, horses and other mammals. Multiple factors impact the transmission and distribution of WNV, related to the dynamics and interactions between pathogen, vector, vertebrate hosts and environment. Hence, among other drivers, weather conditions have direct and indirect influences on vector competence (the ability to acquire, maintain and transmit the virus), on the vector population dynamic and on the virus replication rate within the mosquito, which are mostly weather dependent. The importance of climatic factors (temperature, precipitation, relative humidity and winds) as drivers in WNV epidemiology is increasing under conditions of climate change. Indeed, recent changes in climatic conditions, particularly increased ambient temperature and fluctuations in rainfall amounts, contributed to the maintenance (endemization process) of WNV in various locations in southern Europe, western Asia, the eastern Mediterranean, the Canadian Prairies, parts of the USA and Australia. As predictions show that the current trends are expected to continue, for better preparedness, any assessment of future transmission of WNV should take into consideration the impacts of climate change.

The global ecology and epidemiology of West Nile virus

Since its initial isolation in Uganda in 1937 through the present, West Nile virus (WNV) has become an important cause of human and animal disease worldwide. WNV, an enveloped virus of the genus Flavivirus, is naturally maintained in an enzootic cycle between birds and mosquitoes, with occasional epizootic spillover causing disease in humans and horses. The mosquito vectors for WNV are widely distributed worldwide, and the known geographic range of WNV transmission and disease has continued to increase over the past 77 years. While most human infections with WNV are asymptomatic, severe neurological disease may develop resulting in long-term sequelae or death. Surveillance and preventive measures are an ongoing need to reduce the public health impact of WNV in areas with the potential for transmission.

Systematic analysis of viral genes responsible for differential virulence between American and Australian West Nile virus strains

A variant Australian West Nile virus (WNV) strain, WNVNSW2011, emerged in 2011 causing an unprecedented outbreak of encephalitis in horses in south-eastern Australia. However, no human cases associated with this strain have yet been reported. Studies using mouse models for WNV pathogenesis showed that WNVNSW2011 was less virulent than the human-pathogenic American strain of WNV, New York 99 (WNVNY99). To identify viral genes and mutations responsible for the difference in virulence between WNVNSW2011 and WNVNY99 strains, we constructed chimeric viruses with substitution of large genomic regions coding for the structural genes, non-structural genes and untranslated regions, as well as seven individual non-structural gene chimeras, using a modified circular polymerase extension cloning method. Our results showed that the complete non-structural region of WNVNSW2011, when substituted with that of WNVNY99, significantly enhanced viral replication and the ability to suppress type I IFN response in cells, resulting in higher virulence in mice. Analysis of the individual non-structural gene chimeras showed a predominant contribution of WNVNY99 NS3 to increased virus replication and evasion of IFN response in cells, and to virulence in mice. Other WNVNY99 non-structural proteins (NS2A, NS4B and NS5) were shown to contribute to the modulation of IFN response. Thus a combination of non-structural proteins, likely NS2A, NS3, NS4B and NS5, is primarily responsible for the difference in virulence between WNVNSW2011 and WNVNY99 strains, and accumulative mutations within these proteins would likely be required for the Australian WNVNSW2011 strain to become significantly more virulent.

Single-Stranded RNA Viruses

In this chapter, we describe 73 zoonotic viruses that were isolated in Northern Eurasia and that belong to the different families of viruses with a single-stranded RNA (ssRNA) genome. The family includes viruses with a segmented negative-sense ssRNA genome (families Bunyaviridae and Orthomyxoviridae) and viruses with a positive-sense ssRNA genome (families Togaviridae and Flaviviridae). Among them are viruses associated with sporadic cases or outbreaks of human disease, such as hemorrhagic fever with renal syndrome (viruses of the genus Hantavirus), Crimean–Congo hemorrhagic fever (CCHFV, Nairovirus), California encephalitis (INKV, TAHV, and KHATV; Orthobunyavirus), sandfly fever (SFCV and SFNV, Phlebovirus), Tick-borne encephalitis (TBEV, Flavivirus), Omsk hemorrhagic fever (OHFV, Flavivirus), West Nile fever (WNV, Flavivirus), Sindbis fever (SINV, Alphavirus) Chikungunya fever (CHIKV, Alphavirus) and others. Other viruses described in the chapter can cause epizootics in wild or domestic animals: Geta virus (GETV, Alphavirus), Influenza A virus (Influenzavirus A), Bhanja virus (BHAV, Phlebovirus) and more. The chapter also discusses both ecological peculiarities that promote the circulation of these viruses in natural foci and factors influencing the occurrence of epidemic and epizootic outbreaks

Role of enhanced vector transmission of a new West Nile virus strain in an outbreak of equine disease in Australia in 2011

Background

In 2011, a variant of West Nile virus Kunjin strain (WNV_KUN) caused an unprecedented epidemic of neurological disease in horses in southeast Australia, resulting in almost 1,000 cases and a 9% fatality rate. We investigated whether increased fitness of the virus in the primary vector, Culex annulirostris, and another potential vector, Culex australicus, contributed to the widespread nature of the outbreak.

Methods

Mosquitoes were exposed to infectious blood meals containing either the virus strain responsible for the outbreak, designated WNV_KUN2011, or WNV_KUN2009, a strain of low virulence that is typical of historical strains of this virus. WNV_KUN infection in mosquito samples was detected using a fixed cell culture enzyme immunoassay and a WNV_KUN- specific monoclonal antibody. Probit analysis was used to determine mosquito susceptibility to infection. Infection, dissemination and transmission rates for selected days post-exposure were compared using Fisher’s exact test. Virus titers in bodies and saliva expectorates were compared using t-tests.

Results

There were few significant differences between the two virus strains in the susceptibility of Cx. annulirostris to infection, the kinetics of virus replication and the ability of this mosquito species to transmit either strain. Both strains were transmitted by Cx. annulirostris for the first time on day 5 post-exposure. The highest transmission rates (proportion of mosquitoes with virus detected in saliva) observed were 68% for WNV_KUN2011 on day 12 and 72% for WNV_KUN2009 on day 14. On days 12 and 14 post-exposure, significantly more WNV_KUN2011 than WNV_KUN2009 was expectorated by infected mosquitoes. Infection, dissemination and transmission rates of the two strains were not significantly different in Culex australicus. However, transmission rates and the amount of virus expectorated were significantly lower in Cx. australicus than Cx. annulirostris.

Conclusions

The higher amount of WNV_KUN2011 expectorated by infected mosquitoes may be an indication that this virus strain is transmitted more efficiently by Cx. annulirostris compared to other WNV_KUN strains. Combined with other factors, such as a convergence of abundant mosquito and wading bird populations, and mammalian and avian feeding behaviour by Cx. annulirostris, this may have contributed to the scale of the 2011 equine epidemic.

The Australian Public is Still Vulnerable to Emerging Virulent Strains of West Nile Virus

The mosquito-borne West Nile virus (WNV) is responsible for outbreaks of viral encephalitis in humans and horses with particularly virulent strains causing recent outbreaks in Eastern Europe, the Middle East, and North America. In Australia, a strain of WNV, Kunjin (WNVKUN), is endemic in the north and infection with this virus is generally asymptomatic. However, in early 2011, following extensive flooding, an unprecedented outbreak of WNVKUN encephalitis in horses occurred in South-Eastern Australia, resulting in more than 1,000 cases and a mortality of 10-15%. Despite widespread evidence of equine infections, there was only a single mild human case reported during this outbreak. To understand why clinical disease was seen in horses without similar observations in the human population, a serosurvey was conducted using blood donor samples from areas where equine cases were reported to assess level of flavivirus exposure. The seroprevalence to WNVKUN in humans was low before the outbreak (0.7%), and no significant increase was demonstrated after the outbreak period (0.6%). Due to unusual epidemiological features during this outbreak, a serosurvey was also conducted in rabbits, a potential reservoir host. Out of 675 animals, sampled across Australia between April 2011 and November 2012, 86 (12.7%) were seropositive for WNVKUN, with the highest prevalence during February of 2012 (28/145; 19.3%). As this is the first serological survey for WNVKUN in Australian feral rabbits, it remains to be determined whether wild rabbits are able to develop a high enough viremia to actively participate in WNV transmission in Australia. However, they may constitute a sentinel species for arbovirus activity, and this is the focus of on-going studies. Collectively, this study provides little evidence of human exposure to WNVKUN during the 2011 outbreak and indicates that the Australian population remains susceptible to the emergence of virulent strains of WNV.

Current developments in understanding of West Nile virus central nervous system disease

PURPOSE OF REVIEW

West Nile virus (WNV) is the most important cause of epidemic encephalitis in the United States. We review articles published in the last 18 months related to the epidemiology, immunology, clinical features, and treatment of this disease.

RECENT FINDINGS

There was a resurgence in WNV disease in the United States in 2012. The WNV strain now predominant in the United States (NA/WN02) differs from the initial emergent isolate in 1999 (NY99). However, differences in the genetics of currently circulating United States WNV strains do not explain variations in epidemic magnitude or disease severity. Innate and acquired immunity are critical in control of WNV, and in some cases pathways are central nervous system specific. The clinical features of infection are now well understood, although nonconfirmed observations of chronic viral excretion in urine remain controversial. There is no specific antiviral therapy for WNV, but studies of antivirals specific for other flaviviruses may identify agents with promise against WNV. Phase I and II human WNV vaccine clinical trials have established that well tolerated and immunogenic WNV vaccines can be developed.

SUMMARY

WNV remains an important public health problem. Although recent studies have significantly increased our understanding of host immune and genetic factors involved in control of WNV infection, no specific therapy is yet available. Development of a well tolerated, immunogenic, and effective vaccine against WNV is almost certainly feasible, but economic factors and the lack of predictability of the magnitude and location of outbreaks are problematic for designing phase III trials and ultimate licensure.

Current trends in West Nile virus vaccine development

West Nile virus (WNV) is a mosquito-borne flavivirus that has become endemic in the United States. From 1999-2012, there have been 37088 reported cases of WNV and 1549 deaths, resulting in a 4.2% case-fatality rate. Despite development of effective WNV vaccines for horses, there is no vaccine to prevent human WNV infection. Several vaccines have been tested in preclinical studies and to date there have been eight clinical trials, with promising results in terms of safety and induction of antiviral immunity. Although mass vaccination is unlikely to be cost effective, implementation of a targeted vaccine program may be feasible if a safe and effective vaccine can be brought to market. Further evaluation of new and advanced vaccine candidates is strongly encouraged.